The specific aims of this proposal are: 1) To determine if phenotypically distinct ALL blasts possess cell surface antigens which are also expressed by a cell subset of normal regenerating bone marrow (a putative stem cell population) and to compare these antigens with those on normal lymphoid cells. Cells from regenerating bone marrow will be obtained from patients in remission after anticancer treatment has been stopped. These bone marrow cells and cell subsets will be characterized by their membrane markers, surface antigens and functional properties. 2) To establish if cell surface phenotypes of normal lymphocytes, normal lymphoblasts and neoplastic lymphoid cells correlate with the biochemical and pharmacological characteristics of these cells. 3) To determine in children with ALL the kinetics of recovery of T lymphocyte subsets and their helper or suppressor role upon B cell function after cessation of therapy.